We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.
Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.
708 COLOR SENSITOMETRY June
Integral Color Densities
Three density values are necessary to describe the color of each image, and for images that are to be viewed on the screen these densities should, in principle, be the colorimetric densities described in Section IV. These are the only densities directly related to the international standard scales on which the color of the images would be correctly described. In practice, however, it has been found sufficient to demand that the density numbers used for this purpose should satisfy these simpler requirements : (a) The three densities describing a gray image should be equal, and (b) in describing a nongray image, the differences among three unequal densities should give an approximate indication of its hue and saturation.
Arbitrary three-filter integral densities will not satisfy the first of these requirements; neither will spectral densities. For an accurately gray image in a typical process, Fig. 8 shows spectral densities of 1.06, 1.01 and 0.93. For a given process, it would be possible, of course, to select reading wavelengths such that equal densities would correspond to a gray at least at one density level. Alternatively, it would be possible to compute, for other wavelengths, multiplicative scale factors which would so convert the original densities that equal numbers would correspond to a gray at least at one density level. In direct-reading densitometers, this multiplication might be automatically performed in the indicating circuit. However, either scheme can be expected to work over a large density range only if the original integral densities are approximately monochromatic. Even then, the correction would be imperfect, although the resulting numbers might be useful in many applications. The principal reason for disregarding this possibility has been the interest in analytical density scales, which involve additional objectives in a somewhat different direction.
Before discussing these additional features, the second of our requirements must be briefly considered. Since an image on the film is uniquely specified by any three integral densities, it follows that it must be possible to infer the color of the image from the three density numbers. However, it has been the intent of our requirement that the correlation between these numbers and the color of the image should be easy to visualize and remember. This is not the case in the systems considered in the preceding paragraph. Figure 11 shows a conventional integral density plot in which narrow-band filter densi